Flat panel display and driving method thereof

ABSTRACT

According to the present invention, a flat panel display is provided, which includes a display panel where a plurality of pixels are formed. One pixel includes a first and a second signal lines extending in any one direction and a pixel circuit connected to the first and the second signal lines, and the first and the second signal lines intersect with each other. The pixel circuit includes a plurality of storages, a plurality of first and second switching elements connected to the storages, respectively, and a display cell. The storages store data transmitted through the first signal during predetermined time. The first switching elements send data transmitted through the first signal line to the respective storages in response to a signal transmitted through the second signal line. The second switching elements are sequentially driven during one frame to transmit the data stored in the storages to the display cell. The display cell displays image of the pixel according to the data stored in the storages.

BACKGROUND OF THE INVENTION

(a) Field of the Invention

The present invention relates to a flat panel display and a drivingmethod thereof, and more particularly to a flat panel display includinga plurality of pixels having memory circuits therein and a drivingmethod thereof.

(b) Description of the Related Art

In recent year, as personal computers and television sets becomelight-weighted and slim, so a display is required to be the same. Inorder to fulfill such requirements, flat panel displays such as a liquidcrystal display (“LCD”) instead of a cathode ray tube (“CRT”) aredeveloped.

These flat panel displays include a liquid crystal display (“LCD”), afield emission display (“FED”), a electroluminescent display, and aplasma display panel (“PDP”).

These flat panel displays have a problem of implementing a variety ofgrays. The LCD, which includes an upper panel with a common electrodeand color filters, a lower panel with thin film transistors (“TFTs”) andpixel electrodes, and a liquid crystal layer disposed therebetween,applies different electric potentials to the pixel electrodes and thecommon electrode to generate electric field to change the arrangement ofliquid crystal molecules, thereby controlling the transmittance of lightto implement a variety of grays.

The electroluminescent display implements a variety of grays bycontrolling applied data voltages in several grades in a predeterminedrange since currents corresponding to the data voltages applied to pixelcircuits are applied to electroluminescent devices and theelectroluminescent devices emit light depending on the applied currents.

The PDP implements 2^(N) grays by dividing one frame into N subframes,each subframe including an addressing period for determining whether toimplement grays and a display period for implementing grays, and thendiscriminating display time of each sub-frame by exponent of 2.

Although the above-described driving method for the PDP is applicable toa gray implementation of a flat panel display including pixels driven inactive matrix type, there is a problem that the addressing in eachsubframe yields increased power consumption, the addressing periodreduces the display period, and the display period is limited toexponent of 2.

SUMMARY OF THE INVENTION

Considering this problem, a motivation of the present invention is todecrease the power consumption in gray implementation.

The present invention provides a plurality of storages at a pixel andsequentially drives a display cell with data stored in the storages,thereby accomplishing the motivation.

According to an aspect of the present invention, a flat panel display isprovided, which includes a display panel provided with a plurality ofpixels. A pixel includes first and second signal lines extending inrespective directions and intersecting each other and a pixel circuitconnected to the first and the second signal lines. The pixel circuitincludes a plurality of storages, a plurality of first and secondswitching elements connected to the storages, and a display cell. Thestorages store data from the first signal line during a predeterminedtime. The first switching elements transmit data from the first signalline to the respective storages in response to a signal from the secondsignal line. The second switching elements are sequentially drivenduring a frame to transmit the data stored in the storages to thedisplay cell. The display cell displays image for the pixel according tothe data stored in the storages.

The pixel circuit may further include a plurality of inverting switchingelements for inverting the data stored in the storages to be applied tothe display cell.

The data stored in the storages preferably have a first value making thedisplay cell represent white gray and a second value making the displaycell represent black gray.

The pixel circuit according to the first aspect of the present inventionmay further include a third switching element connected between one ofthe first signal lines and the display cell, and the third switchingelement transmits data representing a variety of grays from the firstsignal line to the display cell in response to a signal from the secondsignal line.

The first signal line may include a plurality of signal lines connectedto the first switching elements, respectively. Alternatively, the firstsignal line may include one signal line and the number of the secondsignal lines may equal to the number of the first switching elements.Alternatively, the first signal line and the second signal line includea plurality of signal lines, respectively, and the first switchingelements may correspond to one of the first signal lines and the secondswitching elements may correspond to one of the second signal lines,respectively.

The address time is a predetermined time shorter than one frame or equalto or longer than one frame.

According to a second aspect of the present invention, a method ofdriving a flat panel display including a plurality of pixels havingdisplay cells is provided. According to the method, data are stored in aplurality of storages during a predetermined address time, respectively.Next, one frame or a portion of one frame is divided into a plurality ofsub-frames and the respective display cells are sequentially driven withthe data stored in the storages during sub-frames, thereby displayinggray.

When data representing still images are inputted, data are stored in thestorages, and when data representing moving images are inputted, thedisplay cells may be directly driven.

Preferably, the data stored in the storages and inverted data arealternately applied to the display cells, thereby driving the displaycells.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an LCD according to a first embodiment of the presentinvention;

FIG. 2 illustrates a single pixel circuit of an LCD according to a firstembodiment of the present invention;

FIG. 3 shows driving waveform for implementing gray in an LCD accordingto a first embodiment of the present invention;

FIG. 4 illustrates a single pixel circuit of an LCD according to asecond embodiment of the present invention;

FIG. 5 illustrates an LCD according to a third embodiment of the presentinvention;

FIG. 6 and FIG. 7 illustrate single pixel circuits of LCDs according tothird and fourth embodiments of the present invention;

FIG. 8 illustrates an LCD according to a fifth embodiment of the presentinvention; and

FIG. 9 and FIG. 10 illustrate single pixel circuits of LCD according tofifth and sixth embodiments of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Now, flat panel displays and driving methods thereof will be describedin detail with reference to accompanying drawings.

First, an LCD and a driving method thereof according to a firstembodiment of the present invention will be described with reference toFIG. 1 to FIG. 3.

FIG. 1 shows an LCD according to a first embodiment of the presentinvention, and FIG. 2 shows a single pixel circuit of an LCD accordingto a first embodiment of the present invention. FIG. 3 shows a drivingwaveform for implementing gray in an LCD according to a first embodimentof the present invention.

As shown in FIG. 1, an LCD according to the first embodiment of thepresent invention includes a liquid crystal panel 100, a gate driver200, and a data driver 300.

The gate driver 200 applies gate signals for selecting pixels of theliquid crystal panel 100 to the liquid crystal panel 100 through aplurality of gate lines G1-Gm.

The data driver 300 applies signals representing images to the liquidcrystal panel 100 through a plurality of groups of data lines D1-Dn, andone data line group Di for one column (i-th column) includes N signallines Di₁-Di_(N). The data voltages applied to the N signal linesDi₁-Di_(N) represent white or black gray.

The liquid crystal panel 100 includes a plurality of pixel circuits 110arranged in a matrix, and each pixel circuit 110 is formed in an areadefined by two neighboring gate lines G1-Gm and two neighboring dataline groups D1-Dn, which is connected to adjacent one gate line and onedata line group.

Now, referring to FIG. 2, a single pixel circuit 110 connected to i-thdata lines Di₁-Di_(N) and a j-th gate line Gj will be described indetail.

As shown in FIG. 2, a single pixel circuit 110 of an LCD according tothe first embodiment of the present invention includes N memory circuitsM₁-M_(N), N addressing switching elements AS₁-AS_(N), N gray switchingelements GS₁-GS_(N), and a liquid crystal cell LC.

Each address switching element AS₁-AS_(N) is connected between a dataline Di₁-Di_(N) and a memory circuit M₁-M_(N), and stores data in therespective memory circuit M₁-M_(N) in response to the gate signals fromthe gate driver 200.

Each gray switching element GS₁-GS_(N) is connected between a memorycircuit M₁-M_(N) and the liquid crystal cell LC, and drives the liquidcrystal cell LC with the data stored in the memory circuit M₁-M_(N) inresponse to driving signals from an external device.

A common electrode, which is one terminal of the liquid crystal cell LC,is supplied with a common electrode voltage Vcom, and the commonelectrode voltage Vcom displays a gray together with a data voltageapplied to a pixel electrode, which is the other terminal of the liquidcrystal cell LC.

The first embodiment of the present invention divides a single frameinto an addressing frame AF and N sub-frames SF1-SFN. In detail, thedata are stored in the memory circuits M₁-M_(N) during the addressingperiod, and then, the liquid crystal cell LC is driven with the datastored in the memory circuits by sequentially driving the gray switchingelements during the sub-frame intervals SF1-SFN.

As described above, when the liquid crystal cell LC is driven with Nsub-frames, it is possible to display a 2^(N) gray image. The period ofsub-frames may be divided into exponent of 2 like an ADS type PDP, or,without being divided into exponent of 2, it may be determined throughsignal processing in consideration of a gamma correction and imagequality improvement.

Now, referring to FIG. 3, a driving method of the LCD according to thefirst embodiment of the present invention will be described.

As shown in FIG. 3, the first embodiment of the present invention drivesdividing a frame into an addressing frame AF and N sub-frames SF1-SFN.

During the addressing frame AF, a gate signal for selecting pixelcircuits of the rows is applied to one of the gate lines GS₁-GS_(N).When the gate signal is applied to j-th gate line Gj, the data voltagesare stored in the respective memory circuits M₁-M_(N) connected to thej-th gate line Gj. That is, the addressing switching elements AS₁-AS_(N)of the respective pixel circuits connected to the j-th gate line areturned on, and thereby, the data voltages applied through the data linesDil-DiN from the data driver 300 are stored in the memory circuitsM₁-M_(N).

After the data voltages are stored in the memory circuits during theaddressing frame AF, the liquid crystal cell LC is sequentially drivenwith the data stored in the memory circuits during the sub-framesSF1-SFN.

In detail, the gray switching element GS₁ of the pixel circuit drivesthe liquid crystal cell LC with the data voltage stored in the memorycircuit M₁ during the first sub-frame SF1 in response to a GG₁ signal,and the gray switching element GS₂ of the pixel circuit drives theliquid crystal cell LC with the data voltage stored in the memorycircuit M2 during the second sub-frame SF2 in response to a GG₂ signal.In this manner, the liquid crystal cell LC is driven with the datavoltages stored in the memory circuits M₁-M_(N) of the pixel circuitduring the sub-frames SF1-SFN.

For example, in case of the LCD in a normally white mode, the datavoltage stored in the memory circuit, if having the same value as thecommon electrode voltage Vcom, represents a white gray, while the datavoltage represents a black gray if it has a value different from thecommon electrode voltage Vcom. In this case, the gray is determined byratio of time for representing the white gray and time for displayingthe black gray. Thus, the first embodiment of the present inventionimplements 2^(N) grays since there are N memory circuits in one pixel.

As described above, the first embodiment of the present invention, whendisplaying still images, stores the data in the memory circuits atfirst, and thereafter, drives the liquid crystal using the data storedin the memory circuits without re-applying the data voltages from thedata driver. In case of displaying moving images, new data are stored inthe memory circuits during each addressing frame, the liquid crystal isdriven using such data.

In the meantime, when a gray is displayed in one frame and another grayis displayed in the next frame, DC bias applied across the liquidcrystal cell LC may deteriorate characteristics of the liquid crystal.To prevent it, generally, an inverting switching element (not shown) forapplying inverted data and inverted common electrode voltage to theliquid crystal cell LC may be employed in the pixel circuit. It isapparent that the above-described inverting switching element is alsoapplicable to other embodiments described below.

Although the first embodiment of the present invention displays grays ofall images using the memory circuits, grays of still images may bedisplayed using the memory circuit while grays of moving images may bedisplayed by directly driving the liquid crystal cell without using thememory circuits.

Referring to FIG. 4, an embodiment using such a driving method will bedescribed in detail.

FIG. 4 shows a single pixel of an LCD according to a second embodimentof the present invention.

As shown in FIG. 4, an LCD according to the second embodiment of thepresent invention has substantially the same configuration as thataccording to the first embodiment except that a pixel circuit 110further includes an analog switching element SW.

The pixel circuit 110 connected to i-th data lines Di and j-th gate lineGj will be described in detail. This pixel circuit 110 further includesan analog switching element SW connected between one signal line (e.g.,Di₁) of data lines Di₁-Di_(N) and a liquid crystal cell LC.

In case of displaying still images, the data are once stored in thememory circuits like the first embodiment of the present invention, andthe liquid crystal is driven using the stored data. In case ofdisplaying moving images, unlike the first embodiment of the presentinvention, addressing switching elements AS₁-AS_(N) and gray switchingelements GS₁-GS_(N) are turned off and the analog switching element SWis turned on. Then, the liquid crystal cell LC is driven with analogdata voltage applied through the data line Di₁. The analog data voltagerepresents a variety of grays as well as white and black grays.

The first and the second embodiments of the present invention store thedata in the respective memory circuits by dividing one data line into aplurality of signal lines. Alternately, the data are stored in thememory circuit by dividing one gate line into a plurality of signallines.

An embodiment of diving one gate line into a plurality of signal lineswill be described in detail with reference to FIGS. 5 to 7.

FIG. 5 shows an LCD according to a third embodiment of the presentinvention, and FIG. 6 and FIG. 7 show single pixel circuits of LCDsaccording to third and fourth embodiments of the present invention.

As shown in FIG. 5, an LCD according to a third embodiment of thepresent invention has substantially the same configuration as thataccording to the first embodiment except for a gate driver 200, a datadriver 300, gate lines G1-Gm, and data lines D1-Dn.

In detail, the LCD according to the third embodiment includes aplurality of gate line groups G1-Gm, each gate line group Gj including aplurality of signal lines Gj₁-Gj_(N). Instead, one data line Di does notinclude a plurality of signal lines unlike the first embodiment.

A pixel circuit 110 connected to an i-th data line Di and j-th gatelines Gj₁-Gj_(N) of the LCD according to the third embodiment of thepresent invention will be described in detail with reference to FIG. 6.

A pixel circuit 110 according to the third embodiment of the presentinvention includes a plurality of addressing switching elementsAS₁-AS_(N) connected between the data line Di and a plurality of memorycircuits M₁-M_(N) as shown in FIG. 6. The addressing switching elementsAS₁-AS_(N) store digital data applied through the data line Di in thememory circuits M₁-M_(N) in response to the gate signals applied throughthe respective gate lines Gj₁-Gj_(N). The storage of the data in thememory circuits M₁-M_(N) is performed during an addressing frame AF likethe first embodiment

A plurality of gray switching elements GS₁-GS_(N) connected between thememory circuits M₁-M_(N) and the liquid crystal cell LC drive the liquidcrystal cell LC with the data stored in the memory circuits M₁-M_(N) inresponse to driving signals GG₁-GG_(N) from an external device. The grayis determined by ratio of time for representing the white gray and timefor displaying the black gray during the entire frame, like the firstembodiment

As shown in FIG. 7, an LCD according to a fourth embodiment of thepresent invention has substantially the same configuration as thataccording to the third embodiment except that a pixel circuit 110further includes an analog switching element SW.

In the fourth embodiment, the pixel circuit 110 connected to i-th dataline Di and j-th gate line Gj according to the fourth embodiment will bedescribed in detail. The pixel circuit 110 further includes an analogswitching element SW connected between one (e.g., Gi₁) of signal linesGi₁-Gi_(N). and a liquid crystal cell LC.

In case of displaying still images, like the first embodiment of thepresent invention, the data are once stored in a plurality of memorycircuits M₁-M_(N), and thereafter, a plurality of gray switchingelements GS₁-GS_(N) is driven to apply the data stored in the memorycircuits M₁-M_(N) to the liquid crystal cell LC, thereby implementingthe grays. In case of displaying moving images, a plurality ofaddressing switching elements AS₁-AS_(N) and the gray switching elementGS₁-GS_(N) are turned off and the analog switching element SW is turnedon to drive the liquid crystal cell LC with analog data voltage appliedthrough the data line Di, thereby implementing the grays.

The first to the fourth embodiments of the present invention store thedata in the memory circuits by dividing one data line into a pluralityof signal lines or one gate line into a plurality of signal lines.However, one data line and one gate line are divided into a pluralitysignal lines for storing the data in the respective memory circuits.

Now, an embodiment of dividing a data line and a gate line into aplurality of signal lines will be described with reference to FIGS.8-10.

FIG. 8 shows an LCD according to a fifth embodiment of the presentinvention, and FIG. 9 and FIG. 10 show single pixel circuits of LCDaccording to fifth and sixth embodiments of the present invention.

As shown in FIG. 8, an LCD according to a fifth embodiment of thepresent invention has substantially the same configuration as thataccording to the first embodiment except a gate driver 200, a datadriver 200 and 300, a plurality of gate lines G1-Gm, and a plurality ofdata lines D1-Dn.

In detail, in the LCD according to the fifth embodiment, one gate linegroup Gj and one data line group Di include a plurality of signal linesGj₁-Gj_(P) and a plurality of signal lines Di₁-Di_(Q), respectively. Themultiple of the number (P) of the signal lines included in a gate linegroup and the number (Q) of the signal lines included in a data linegroup is preferably equal to or larger than the number of the memorycircuits (P×Q≧N).

A pixel circuit 110 connected to an i-th data line Di₁-Di_(P) and j-thgate lines Gj₁-Gj_(Q) of the LCD according to the fifth embodiment ofthe present invention will be described in detail with reference to FIG.9.

As shown in FIG. 9, a plurality of addressing switching elementsAS₁-AS_(P) connected to memory circuits M₁-M_(P) are connected to datalines Di₁-Di_(P), respectively, and store data applied through the datalines Di₁-Di_(P) into the memory circuits M₁-M_(P) in response to gatesignals applied through the gate lines Gj₁. Similarly, a plurality ofaddressing switching elements AS_(P+1)-AS_(2P) are connected between thedata lines Di₁-Di_(P) and the memory circuits M_(P+1)-M_(2P), and storedata applied through data lines Di₁-Di_(P) in the memory circuitsM_(P+1)-M_(2P) in response to signals applied through gate lines Gj₂. Inthis way, it is possible to store the data in all of the memory circuitsM₁-M_(P), M_(P+1)-M_(2P), . . . , M_(N).

As described above, the storage of the data in the memory circuits isperformed during interval of the addressing frame AF like the firstembodiment. Since the step of driving a liquid crystal cell LC with thedata stored in the memory circuits M₁-M_(N) is the same process as thefirst embodiment, the description thereof will be omitted.

A sixth embodiment of the present invention implements grays of stillimages by driving a liquid crystal cell using memory circuits, whileimplements grays of moving images by directly driving the liquid crystalcell without using memory circuits like the second and the fourthembodiments.

In detail, as shown in FIG. 10, a pixel circuit 110 of an LCD accordingto the sixth embodiment of the present invention further includes ananalog switching element connected between one data line (e.g., Di₁) anda liquid crystal cell LC. In case of implementing grays of movingimages, the analog switching element SW is driven according to a gatesignal applied through one gate line (e.g., Gj₁) and directly drives theliquid crystal cell with data applied through the data line Di₁.

Although the first to the sixth embodiments store the data in the memorycircuits regarding a predetermined time within one frame as anaddressing frame AF, it is also possible to store data in the memorycircuits regarding one or more frames as an addressing frame AF.

In addition, although LCDs are described as an example of flat paneldisplays, the present invention is not limited to this but is alsoapplicable to flat panel displays of driving pixels in an active matrixtype. The plat panel displays include all of the flat panel displayscapable of implementing grays by average of time to drive displaymaterial, such as a FED and an electroluminescent display.

According to the present invention, it is possible to drive the flatpanel display using the data stored in the memories without applying newdata whenever driving the flat panel display when displaying stillimages. Therefore, it is possible to decrease the power consumptionsince there is no need of applying new data each time when displayingstill images.

1. A flat panel display comprising: a display panel provided with aplurality of pixels arranged in a matrix, one of the pixels including atleast one first signal line extending in a direction, at least onesecond signal line crossing the first signal line, and a pixel circuitconnected to the first signal line and the second signal line, whereinthe pixel circuit comprises: a plurality storages storing datatransmitted through the first signal line during an addressing time; aplurality of first switching elements connected to the storages andtransmitting the data from the first signal line to the storages inresponse to signals from the second signal line; a display celldisplaying images for the pixel according to the data stored in thestorages; and a plurality of second switching elements connected to thestorages and driven in sequence during a frame to send the data storedin the storages to the display cell.
 2. The flat panel display of claim1, wherein the data stored in the storages has a first value making thedisplay cell represent white gray and a second value making the displaycell represent black gray.
 3. The flat panel display of claim 1, whereinthe pixel circuit further comprises a third switching element connectedbetween one of the first signal lines and the display cell andtransmitting data representing a variety of grays from the one of thefirst signal line to the display cell in response to a signal from thesecond signal line, wherein the data stored in the storages has a firstvalue making the display cell represent white gray and a second valuemaking the display cell represent black gray.
 4. The flat panel displayof claim 1, wherein the first signal line includes a plurality of signallines connected to the first switching elements.
 5. The flat paneldisplay of claim 1, wherein the first signal line includes a singlesignal line connected to the first switching elements, and the number ofthe at least one second signal line is equal to the number of the firstswitching elements.
 6. The flat panel display of claim 1, wherein thefirst signal line and the second signal line include a plurality ofsignal lines, respectively, and the first switching elements correspondto one of the first signal lines and one of the second signal lines. 7.The flat panel display of claim 1, wherein the pixel circuit furthercomprises a plurality of inverting switching elements inverting the datastored in the storages to be applied to the display cell.
 8. The flatpanel display of claim 1, wherein the address time is a predeterminedtime shorter than one frame or equal to or longer than one frame.
 9. Adriving method of a flat panel display including a plurality of pixelshaving display cells, the method comprising: a first step of storingdata into a plurality of storages formed in the pixels during apredetermined time; and a second step of implementing grays by dividingone frame or a portion of one frame into a plurality of sub-frameshaving different durations and sequentially driving the display cellswith the data stored in the storages during the sub-frames.
 10. Thedriving method of claim 9, wherein the address time is a portion of oneframe or at least one frame.
 11. The driving method of claim 9, whereinthe second step drives the display cells by alternately applying thedata stored in the storages and inverted data to the display cells. 12.The driving method of claim 9, wherein the data stored in the storageshas a first value making the display cell represent white gray and asecond value making the display cell represent black gray.
 13. Thedriving method of claim 9, wherein the first step is performed such thatwhen data representing still images are inputted, the data are stored inthe storages, and when data representing moving images are inputted, thedisplay cells are directly driven.
 14. The driving method of claim 13,wherein the data representing the still images has a first value makingthe display cell represent white gray and a second value making thedisplay cell represent black gray, and the data representing movingimages has a value making the display cells represent a variety ofgrays.